I was double checking all of the tests in the File system and see that a bunch were not included from one file: DirectoryTest.php. The attached patch converts those as well. I have confirmed that all other tests in File system are correct after this gets in.

All of the changes in #5 look good, but I found a couple of stray t()'s around assert messages in UnmanagedCopyTest.php, lines 42, 86. Maybe they were added by a recent commit, I don't know. If they can get taken care of, then I'll make sure to re-test.